Injection mandrel

ABSTRACT

An injection mandrel and method for introducing treating fluids into a well comprise a center pocket mandrel having a check valve in fluid communication with treating fluid in the annulus of the well and with a chemical injection valve in the mandrel. Treating fluid is pumped through the check valve and the chemical injection valve into the produced fluids in the mandrel, while reverse flow is prevented. In another embodiment a dip tube communicating with the injection valve pocket places treating fluid at a preselected location in the well.

BACKGROUND OF THE INVENTION

The invention relates generally to subsurface well treating apparatusand operations. In particular, the invention relates to an injectionmandrel and method for circulating well treating fluids into subsurfacewells to treat produced fluids from subsurface earth formations.

In order to complete oil and gas wells, subsurface earth formations areperforated to bring the wells into production. The fluids produced maysubject the subsurface and surface equipment to corrosion from a varietyof chemical agents present in the fluids. To combat this corrosion, anumber of well-known corrosion inhibitors may be circulated through thewellbore to reduce or prevent the undesirable effects of the corrosiveagents.

Produced fluids also may contain salts and other dissolved andundissolved solids which can precipitate and deposit on the surface ofthe production tubing or in the perforations in the subsurface earthformation. As deposits build, production flow becomes restricted. Tocombat this problem, one or more of a number of well-known solvents maybe circulated through the well to dissolve any flow restricting depositsand to prevent deposits from recurring.

Apparatus and methods are known to circulate such treating fluidsthrough wells at various depths in the wells. Side-pocket mandrels maybe utilized for this purpose. A treating fluid is injected into theannulus of a well above a packer assembly, through ports in theside-pocket of the mandrel, through a chemical injection valve set inthe side-pocket, and into contact with the produced fluids flowing outof the well. Once the fluids have been treated, they flow through themandrel and production tubing to the surface for recovery.

Side-pocket mandrels suffer from several shortcomings when used for theabove purpose. First, side-pocket mandrels require complicated kickovertools to set and retrieve chemical injection valves in their side valvepocket. Current kickover tools require involved wireline operationswhich are typically not practical at depths below about 15,000 feet.Second, the construction of a side-pocket mandrel does not permitcirculation of the treating fluid below the packer assembly because themandrel does not extend below the packer. Third, side-pocket mandrelsallow untreated, often corrosive, produced fluids into the upper annulusof the well above the packer assembly when the chemical injection valveis not in place. In the annulus, such produced fluids could damage thetubing, casing and other equipment, such as a subsurface safety valve.

Other designs have also been proposed, but these designs suffer from thesame or other shortcomings. The other shortcomings include limitationson the ability to circulate treating fluids at any desired depth in awell, limitations on conducting perforating, logging or other operationswithout having to pull the mandrel from the well, and limitations onflow through the mandrel, which may cause pressure losses and erosionproblems.

Ideally, an apparatus for treating produced fluids in a wellbore willhave the following characteristics. The annulus, the space between theproduction tubing and the casing, above the packer should be effectivelyisolated from produced fluids. The apparatus should be capable ofcirculating treating fluids across the perforations or at any otherpreselected depth. The apparatus should be capable of being routinelyset and operated at total depths in excess of 15,0090 ft. There shouldbe a capability for conducting workover operations through theapparatus. Restrictions to flow should be minimized.

SUMMARY OF THE INVENTION

The present invention is a mandrel and method for circulating a treatingfluid in a well. Preferably, the mandrel is a center-pocket mandrel.

The injection mandrel preferably comprises a body having a longitudinalflow conduit therethrough, a valve pocket in the body substantiallyaxially aligned with the bore of the well and the production tubing andadapted to receive a removable chemical injection valve, a check valvemounted on the body, and a conduit for permitting fluid communicationbetween the check valve and the chemical injection valve. The body isadapted to be attached to a production tubing string. It may be put inthe well through and engaging a packer assembly.

With a chemical injection valve set in the valve pocket, treating fluidis injected into the annulus of the well above the packer assembly. Thistreating fluid flows from the annulus, through the check valve into thevalve pocket, through the chemical injection valve and into contact withthe formation fluid from the lower interval of the well. The treatedformation fluid flows upwardly through the mandrel and the tubing stringto the surface for recovery. The check valve prevents formation fluidsfrom entering the annulus.

The chemical injection valve may be removed using standard wirelinetools and workover operations can be conducted through the valve pocket,since it is substantially aligned with the well tubing bore.

In order to inject treating fluids at any preselected depth below themandrel, a dip tube may be connected to the lower end of the injectionvalve housing. Treating fluids from the annulus may then be pumpedthrough the dip tube to the desired depth for injection into theformation fluids.

The present invention allows chemical injection valves to be routinelyset and retrieved at depths much greater than 15,000 feet and precludesentry of the untreated producing fluids into the upper annulus above thepacker assembly. Treating fluids may be circulated in the well at anydesired depth, and allows a variety of workover and logging tools to berun through the apparatus when the chemical injection valve is removed,so that other downhole operations may be conducted without removing thetubing from the well.

These and other features and advantages of the present invention will bemore readily understood by those skilled in the art from a reading ofthe following detailed description with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 1A and 1B are schematic elevational views of a first embodimentof an injection mandrel in accordance with the present invention.

FIG. 2 is a longitudinal section of the first embodiment of theinjection mandrel in accordance with the present invention.

FIG. 3 is a longitudinal section of the first embodiment of theinjection mandrel in accordance with the present invention, including adip tube.

FIGS. 4, 4A and 4B are detailed longitudinal sections of a secondembodiment of an injection mandrel in accordance with the presentinvention.

FIG. 5 is a horizontal section of the second embodiment of the injectionmandrel taken along line 5--5 of FIG. 4B.

FIG. 6 is a horizontal sectional view of the first embodiment of theinjection mandrel taken along line 6--6 of FIGS. 2 and 3.

FIG. 7 is a horizontal sectional view of the first embodiment of theinjection mandrel taken along line 7--7 of FIG. 2.

DETAILED DESCRIPTION

Referring now to the drawings in more detail, Particularly to FIGS. 1,1A and 1B, there is illustrated a schematic elevational view of aninjection mandrel in accordance with the present invention. Preferably,the mandrel is a center pocket mandrel. A well 10 is shown in which acasing 11 has been cemented, indicated at 12, and perforated in aproducing zone 13. At the surface a Christmas tree 14 is mounted on awellhead 15 on top of the casing 11. A tubing string 20 is suspendedfrom the wellhead 15. A valved conduit 21 is connected to the upper endof the tubing string 20 and a second valved conduit 22 is connectqd intothe wellhead 15 to communicate with the annulus between the inside ofthe casing and the outside of the tubing string. A center pocketmandrel, 24a in FIG. 1A and 24b in FIG. 1B, is connected to the tubingstring 20. A packer assembly 26 seals off and divides the well 10 intoan annulus 14 between the casing 11 and the tubing string 20 (andbetween the casing 11 and center pocket mandrels 24a and 24 b) and alower interval 23 below the packer assembly 26.

Fluids from the producing zone 13 may contain corrosive agents such ashydrogen sulfide, carbon dioxide or water which can damage the casingstring 11, tubing 20 and other subsurface and surface equipment. Tocombat this corrosion problem, a suitable corrosion inhibitor may beinjected into the well. Suitable corrosion inhibitors are well known inthe art.

The fluids from the producing zone 13 may also contain salts or otherdissolved and undissolved solids which can precipitate and deposit inthe perforations or tubing string 20, reducing production. To combatthis problem, a suitable solvent may be injected into the well todissolve the deposits. Such solvents are also well known in the art.

As illustrated in FIGS. 1A and 1B, the center pocket mandrels 24a and24b are provided for these and for other operations in which it isdesired to circulate a treating fluid from the annulus 14 of the well 10into contact with the formation fluid in the lower interval 23. Thepresent invention is, therefore, not limited in scope solely to the useof corrosion inhibitors or solvents.

Referring to FIGS. 1 and 1A, a suitable treating fluid is pumped throughthe valved conduit 22 and injected into the annulus 14. From the annulus14, the treating fluid enters the center pocket mandrel 24a through acheck valve, described hereinafter, flows into the valve pocket in thevalve housing of the center pocket mandrel 24a and into the bore of themandrel to contact the formation fluids from lower interval 23. Thetreated formation fluid is circulated upward through the flow conduit 25and to the tubing string 20 and the surface for recovery through thevalved conduit 21.

If it is desired to treat formation fluids at a depth below the packerassembly 26, for example at the depth of producing zone 13, the modifiedcenter pocket mandrel 24b of FIG. 1B may be utilized. The flow oftreating fluid is the same as described above, with the followingexception. A dip tube 25 is connected to the valve pocket. The dip tubeextends below the mandrel into the producing zone 13.

Specific embodiments of injection mandrels in accordance with thepresent invention are shown in greater detail in FIGS. 2-7. It should benoted that the embodiments comprise many common elements, some identicalin construction and others similar but modified for the specificembodiment. The identical elements of the various specific embodimentshave common numbering throughout this detailed discussion. The similarbut non-identical elements will also have common numbering including aletter identifier for the particular embodiment.

Referring to FIG. 2, there is illustrated in detail a center pocketmandrel in accordance with the invention and corresponding to theembodiment depicted in FIG. 1A. The center pocket mandrel 30 comprises atubular body 32, an exterior check valve 34, a conduit 36 for fluidcommunication between the check valve 34 and a valve housing 33 defininga valve pocket 38 in the body 32. A removable chemical injection valve40 is set in the valve pocket 38 for permitting fluid communication fromthe valve pocket 38 into the formation fluid. The lower end of thechemical injection valve is preferably recessed in, or enclosed by, thevalve housing to create a dead space to thereby reduce wear andcorrosion of the injection valve by the produced fluids flowing upwardlythrough the mandrel. A longitudinal flow conduit 42 through the mandrelbody 32 transmits treated formation fluid through the mandrel 30 andtubing string 20 FIG. 1A) for collection at the surface. The flowconduit 42 is defined by the inner surface of the body 32 and the outersurface of the valve housing 33 that is attached to the inner surface ofthe mandrel body 32.

The body 32 has threaded ends 44, 94 for connection to the tubing string20, a lower section 46 for the chemical injection valve 40, and atapered upper section 48 between the lower section 46 of the body andthe upper threaded end 44. The tapered upper section of the body reducesturbulence in the produced fluid flow to minimize wear on the mandrel atthis point.

A mounting lug 58 having a slanted upper surface 60 is connected to theinside surface of the body 32 and the exterior of the valve housing 33,with the slanted upper surface 60 above the top of the valve housing 33.The lug 58 provides additional support for the valve housing 33 and theslanted upper surface 60 directs chemical injection valves 40 (ordownhole tools) into or through the valve pocket 38. The valve housing33 has an inwardly beveled upper edge 62 for the same purpose.

The treating fluid conduit 36 is mounted to the exterior wall of thelower body section 46. The conduit 36 comprises a flow passage from thecheck valve 34,.through a fluid port 66 through the mandrel body, andinto the valve pocket 38. Referring to FIGS. 2 and 7, it can be seenthat the conduit 36 may comprise a tube welded or otherwise mounted tothe exterior wall of the lower body section 46 on the side adjacent thevalve housing 33.

The check valve 34 allows fluid to flow from the annulus 14 of the well10 through the conduit 36 and into the valve pocket 38, but precludesfluid flow in the opposite direction. The check valve 34 may be any ofthe well known one-way or check valves commonly used in injectionoperations. The preferred choice is a unit consisting of two ball andseat check valves in series. Ball and seat valves will allow fluid flowwhen the pressure in annulus 14 rises to a preselected value in excessof the fluid pressure in the valve pocket 38. Spring loaded check valvesmay also be used. Such one-way valves and valve arrangements arewell-known to those skilled in the art. The set point of the check valvewill need to be selected so that the check valve will permit flow intothe mandrel when there is a preselected differential pressure betweenthe fluid in the annulus and the fluid in the mandrel.

The check valve 34 is connected to one end of the conduit on theexterior wall of the lower body section 46 at a point below the fluidport 66. Alternatively, at least a part of the conduit should be belowthe port 66. These arrangements will form a gas trap in the conduit 36,preventing produced fluids, such as corrosive gases, from entering theconduit and minimizing the chances of damage to the check valve 34.

Once the treating fluid has entered the valve pocket 38, it flowsthrough ports 70 into a longitudinal bore 68 in the chemical injectionvalve 40. The longitudinal bore 68 houses one or more one-way or checkvalves 72 which allow the treating fluid to flow through an opening 73in the end of the chemical injection valve 40 and into contact with theformation fluids. The check valves 72 may be of any of the typescommonly used in injection operations and familiar to those skilled inthe art. The preferred choice is again a ball and seat arrangement whichmay be used singly or in series plurality.

The injection valve 40 is inserted and removed from the valve housing 33by standard wireline operations. The injection valve 40 is provided witha fishing neck 74 for attachment to a wireline and a locking assembly 76which is used to secure chemical injection valve 40 in place in thevalve housing 33. The fishing neck 74 and locking assembly 76 may be anyone of the number of well known arrangements familiar to those skilledin the art. The locking assembly 76 is provided with dogs 78 which, wheninserted into inner tube 52, rest on shoulders 80 thereof to secure thevalve 40 in place in the valve housing 33.

Above and below ports 70, the chemical injection valve 40 is providedwith fluid seals 82, which may comprise any of the number of well knownfluid seals such as, for example, chevron seals or O-rings. As thechemical injection valve 40 is inserted into the valve pocket 38, fluidseals 82 contact shoulders 84 on the interior wall of the valve housingto form a fluid seal. This seal insures treating fluid will flow throughthe ports 70 and out of the chemical injection valve 40.

Deflector lugs 92 are provided on the exterior wall of lower bodysection 46 aligned with the check valve 34 to prevent the valve fromcontacting the casing 11 or any obstructions in the well 10 when theinjection mandrel is run into the well. Similar deflector surfaces 93are provided adjacent the upper and lower ends of the conduit.

The end of the lower body 46 has threads 94 for engaging a packerassembly 26 or for connection to tubing or other downhole tools (notshown) which may be attached to the center pocket mandrel 30.

Referring now to FIG. 1, 1A and 2, in the operation of the apparatus ofFIG. 2, the center pocket mandrel 30 is inserted into a well 10connected to the end of tubing string 20 and engaging the packerassembly 26. The check valve 34 is positioned above the packer assembly26.

The chemical injection valve 40 may be in place when the mandrel is runinto the well 10. Alternatively a wireline (not shown) may be attachedto the fishing neck 74 and the chemical injection valve 40 lowered intothe well through the tubing string 20.

The chemical injection valve 40 is then set in the valve housing usingstandard wireline methods. The chemical injection valve 40 is preferablyconstructed so that when dogs 78 are seated, the injection valve ports70 will be adjacent the treating fluid port 66. Once the chemicalinjection valve 40 is in place and secured within the valve pocket 38,the wireline is removed in the usual manner.

The desired treating fluid is then introduced into the annulus 14 of thewell. The fluid pressure in the annulus may then be increased until itis at the preselected value in excess of the fluid pressure in the valvepocket 38. The treating fluid from the annulus then flows through thecheck valve 34, the conduit 36 and the fluid port 66 into the valvepocket 38.

As the fluid pressure rises above the fluid pressure in the lowerinterval 23, the treating fluid in the valve pocket flows through theports 70, the longitudinal bore 68 and the check valves 72 of thechemical injection valve 40 and into contact with the formation fluid.The check valves 72 in the chemical injection valve 40 prevent flow inthe opposite direction.

Formation fluid from lower interval enters the center pocket mandrel 30through the end 96 of the lower body 46 and contacts the treating fluidexiting the chemical injection valve 40. The treated formation fluidthen flows upwardly through flow conduit 42 and the tubing string 20 tothe surface for recovery.

A modification of the center pocket mandrel described above isillustrated in FIG. 3 and corresponds to the embodiment depicted in FIG.1B. The center pocket mandrel 30a illustrated in FIG. 3 and the centerpocket mandrel 30 illustrated in FIG. 2 are nearly identical inconstruction. The difference is the construction of the valve housings38a. The operation of the center pocket mandrels 30a and 30 is alsonearly identical. The following discussion will cover the differencesbetween the two embodiments, and reference may be had to the priordiscussion of the center pocket mandrel for other details.

Referring to FIG. 3, the valve housing 33a is connected to dip tube 98by threads, welding or any suitable means. The dip tube 98 is threaded100 for connection to additional joints of dip tubing to extend the diptube 98 to any preselected depth. This allows treating fluid to beinjected directly into the lower interval 14 at any point below thepacker assembly 26 (FIG. 1B) such as at the depth of the perforations inthe producing zone 13.

The treated formation fluid enters the flow conduit 42a of center pocketmandrel 30a through the opening 96 at the base of the lower body 46.Upon entering center pocket mandrel 30a, this fluid flows upwardlythrough flow conduit 42 and tubing string 20 to the surface forrecovery.

A second embodiment of a center pocket mandrel in accordance with thepresent invention is illustrated in FIG. 4. This embodiment is useful inoperations where the diameter of the casing 11 (FIG. 1A) is such that acenter pocket mandrel with a smaller outside diameter should be used.

The center pocket mandrel 30b in FIG. 4 and 7, and the center pocketmandrel in FIGS. 2 and 6 are nearly identical in construction except forthe placement of their conduits 36 and 36b. The operation of the centerpocket mandrels 30b and 30 is also essentially identical. The discussionbelow will therefore relate only the differences between the twoembodiments, and reference may be had to the prior discussion for otherconstruction and operation details.

The mandrel of this embodiment requires a special lower body section46b. The lower body section is preferably attached to the mandrelhousing 46 by welding 47. A port 49 is machined through the lower bodyto connect the conduit 36 and a check valve manifold 51. The manifold isthreaded or otherwise adapted to accept a check valve 34.

Referring to FIG. 4, conduit 36b is mounted inside the lower bodysection 46 between the outer surface of the valve housing 33 of theinside surface of the body 46. The check valve 34 is in fluidcommunication with the conduit and is mounted on the outer surface ofthe mandrel body 46. Referring to FIGS. 4 and 5, the conduit 36b extendsthrough the flow conduit 42b and into the valve pocket 38 through thefluid port 66b. The rest of the details of this embodiment are the sameas in the embodiment described above. By routing the treating fluidconduit through the inside of the mandrel, a smaller diameter mandrel ispossible.

The mandrels of the present invention provide effective tools forinjecting treating fluids into wells to treat fluids from producingformations. The ability to insert and remove chemical injection valvesby standard wireline procedures allows the center pocket mandrel to beset at depths where side-pocket and other mandrels could not practicallybe used. Use of a dip tube allows the center pocket mandrel to be set ata selected depth while permitting injection of treating fluid into thewell at any depth below the center pocket mandrel.

The exterior check valve (and the chemical injection valve) preventformation fluid from entering the annulus of the well above the packerassembly. This is important to maintain the integrity of any subsurfacesafety valves in the tubing string and to minimize potential problemsdue to pressure leakage.

The center pocket mandrels of the present invention permit otherdownhole operations to be conducted below the mandrel by removing thechemical injection valve from the valve housing. A number of downholetools such as well logging or perforating guns can be lowered throughthe valve pocket to conduct operations below the mandrel.

Many modifications and variations may be made in the techniques andstructures described herein and depicted in the accompanying drawingswithout departing substantially from the concept of the presentinvention. In particular, it is recognized it is possible to modify aside pocket mandrel to include the check valve and certain otherfeatures of the invention and thereby practice the invention.Accordingly, it should be understood that the form of the inventiondescribed and illustrated herein is exemplary only, and is not intendedas a limitation on the scope thereof.

We claim:
 1. A center pocket injection mandrel for circulating treatingfluid from a supply of such fluid in the annulus of a well through aseparate chemical injection valve having a lower end and into a fluidproduced from said well, comprising:a body having a longitudinal flowconduit therethrough for the produced fluid and a port through the bodycommunicating with the annulus of the well, and adapted to be attachedto a tubing string; a valve housing in the body in fluid communicationwith the flow conduit in the body and the port through the body,defining a valve pocket in the body adapted to receive a separatechemical injection valve; and a check valve connected to the body forpermitting flow of the treating fluid from the annulus to the valvepocket through the port in the body and for preventing reverse flow,whereby when a chemical injection valve is in the valve pocket, treatingfluid may be flowed through the check valve and the chemical injectionvalve into contact with the produced fluid and when there is no chemicalinjection valve in the pocket, the check valve prevents flow of producedfluids through the check valve into the annulus of the well.